LabMed

Euthyroid Sick Syndrome

At a Glance

Euthyroid sick syndrome is diagnosed in patients with low thyroid hormone levels suffering from some nonthyroidal systemic illness that may include nutritional deficits, kidney disease, liver disease, malignancy, trauma, or infection. This is commonly seen in the hospital setting and intensive care units, in particular. These patients are usually clinically euthyroid.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Laboratory tests that uncover suspected euthyroid sick syndrome in patients with nonthyroidal systemic illness include thyroid stimulating hormone (TSH), total triiodothyronine (T3), free T3 (fT3), total thyroxine (T4), and free thyroxine (fT4). TSH is a glycoprotein with an alpha and beta subunit. TSH is secreted by the anterior pituitary gland as a result of a negative feedback loop involving T3 and T4. The most common early change in nonthyroidal illness is a decreased T3 or fT3 and a normal or mildly depressed TSH. Total T4 may also be low, but fT4 will most often remain normal. During recovery from the illness, T4 will normalize first and TSH may rebound to slightly elevated levels. Serum cortisol can also be obtained and should be elevated in euthyroid sick syndrome distinguishing this from hypothyroidism secondary to pituitary-hypothalamic disease. (Table 1)

Table 1.

Test Results Indicative of the Disorder
TSH total T4 total T3 Cortisol
0.5 - 5.0 mclUnits/mL <5.0 mcg/dL <80 ng/dL >25 mcg/dL (am), >14 mcg/dL (pm)

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Assessment of thyroid status can be difficult in acutely ill patients and, in general, should not be done. Hospitalized patients may have transiently low or high TSH. TSH levels can be suppressed during treatment on glucocorticoid or dopamine therapy, whereas other drugs, such as amiodarone, can increase TSH levels. Increases in T3 and T4 may occur with ingestion of large quantities of exogenous thyroid hormone.

What Lab Results Are Absolutely Confirmatory?

The pattern of normal TSH and reduced T3/T4 suggests a diagnosis of euthyroid sick syndrome.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

If TSH is slightly elevated or the diagnosis remains unclear, serum cortisol can also be obtained and should be elevated in euthyroid sick syndrome distinguishing this from hypothyroidism secondary to pituitary-hypothalamic disease.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

The clinical setting must be considered when interpreting TSH, T3, and T4. Patients with euthyroid sick syndrome are clinically euthyroid but likely present with some other nonthyroidal systemic illness. Critically ill euthyroid patients may be differentiated from hypothyroid patients, because the latter show very high TSH values, but, as previously mentioned, pharmacotherapeutics can inflate TSH levels, and this too should be considered when making the diagnosis of euthyroid sick syndrome.

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